A pinion carrier is a support structure that locates pinion (or planet) gears in a planetary gear set and transmits torque to other components within a vehicle transmission. A drive shell or planet carrier is a tubular metal component that carries torque from the pinion carrier to another component axially displaced from the pinion carrier in the transmission. The drive shell also revolves around the central axis of the pinion carrier and supports the pinion gears.
Some known methods for producing a pinion carrier include progressively stamping a cup and an end plate and welding the two pieces together; producing powdered metal components which are brazed or bolted together; or cold forming a cup which is welded to a stamped plate.
Current methods for producing a drive shell include deep drawing sheet metal to a tubular shape and forming splines on an inner wall thereof, and cutting a thin walled tube to length and forming splines on an inner surface thereof.
Known methods of producing a combined carrier and drive shell include progressively stamping cups from metal stock having different diameters which are then welded together facing each other. The inner cup is used as the pinion carrier, and the outer cup is used as the drive shell.
In respect of the practices listed above, several problems are experienced in forming the pinion carrier portion of the assembly. Due to the brittle nature of powdered metal parts, the cross-section of the portion of the pinion carrier that separates the retaining faces must be structurally large. During the manufacturing process, a grain density variation is created at the bases of the portion of the pinion carrier that separate retaining faces where it meets much thinner retaining faces. This density variation, along with the concurrent thickness change in the same area, results in a stress riser that frequently causes fracture and failure of the component. To counteract this, the legs and retaining faces must be made thicker than would be needed when produced from wrought material in order for the part to survive its application. This results in increased weight and space consumption, both of which are expensive and undesirable in an automatic transmission environment.
For stamped parts, the production method provides more flexibility than powdered metal and generally reduces space consumption by comparison. However, there is no ability to significantly change the material thickness for any component of the assembly. Therefore, the entire part will be the same thickness as that portion of the assembly needing the most strength. The result is excess mass and space consumption, although it represents a large improvement in these aspects as compared to parts produced from powdered metal. The biggest weakness of stamped parts is the lack of stiffness. Under heavy loading, the stamped parts frequently deflect to the point that the gears may become misaligned causing undesirable noise and wear.
For cold formed parts, improved stiffness is experienced over stampings, and the process can create various material thicknesses in different locations on the components. Therefore, it can minimize overall mass while concentrating material in critical areas. Furthermore, tooling is comparable to that for powdered metal and far less expensive and complex than that required for stamping. The level of detail achievable in cold forming is good enough that many applications require no machining other than creating the pinion shaft holes after forming. However, cold forming is somewhat limited in its ability to create long extrusions cost-effectively.
It would be desirable to produce a torque transmitting assembly wherein production efficiency is maximized and weight and production costs are minimized.